Treatment of cast iron



.. Patented Jan. 18, 1944 UNITED STATES PATENT oFFlcE.

Alfred L. Boegehold,- Detroit, Micli assignor to General Motors Corporation, Detroit, Mich., a corporation .of Delaware No Drawing. Application August 25, 1941,

Serial No. 408,208 I 17 Claims.

ment of cast iron with compounds containing nitrogen.

I have found that cast irons can'be treated while in the molten or fused condition with compounds containing nitrogen, to produce cast iron articles having properties especially useful for particular applications. Cast irons when treated in accordance with the invention contain iron The composition of the cast iron to be treated carbide which is extremely stable under the inwith nitrogen containing compounds to produce fluence of high temperatures. This property is heatresistant castings or articles will vary tievaluable in irons used for many purposes where pending on the particular usage thereof. ,The' exposure to heat is involved. A few examples of amountof the nitrogen containin p und q' articles in which thispropertyis of advantage 1 may bevaried. somewhat dependin n he 110m: are: grate bars, ingot molds, "annealing boxes, position of the fused cast iron and On he prop: chilled iron articles for many purposes, etc. The erties desiredin the final article. In-all cases a' invention herein resides both in the'treated cast relatively small amount of the nitrogen contain v iron and in the method of treating the iron. ins ,compound is us n a y ca e thetotelp lnicarrying out the method in accordancewith' nitrogen i itrdsnco po m is t-Q A the invention the cast iron is melted inany suitto 0.1% by weight otthe cast rpn tr a t b'yable melting furnace and while in the molten A tvpi pos t' or a r nt w stat is treated with a ti l Small amount; cast iron article in accordance: with th inv ntion of a compound containing nitrogen. The nitrois! Carbon -3- silicuu 0,1-,2 n gen compound conveniently may be a nitrided 'ganese' -0 7 Sulphur 1 ma imum. iron powder which is added to the molten cast phosphorus 020% m nitrogen. i mo t m h molten t iron also may b treat d" resulting from addition of 1.00% nitridediron, or by bubbling ammonia gas therethrough. Other" by p f a s s u o t 17 p unds of nitrides and other compounds containing nitrogen molten metal f ia 4, to 12 minutes at a rate may also be used within the scope of the invenof 12 bi te h na d' e e i n. tion. For example, small amounts of such comn t q e p the nitridedi 60!!- pounds as ammonium carbonate and ammonium venientlvmayfl niirided iron' powder c mchloride may be used to" treat the molten iron. If Dosedlargely 0f FEZN- e I desired, two or more of the nitrogen containing AS a u m example of the c flu addicompounds may be used in combination in'treat- 'tiuu f amitl'ogeu compound molten cast ing'th lt i e iron in stabilizing'iron. carbide, the following is The nitrogen containing compound may be n;

. l a 7' a added to the molten cast iron in many different To i' d i e t ma i on n ev ways. The preferred method in any particular d o p 0 %;..ca b0 silicon. application. will depend on a number of factors 40 .37 anganese, lOWs p a D Ph HIS and ordinarily will vary with the apparatus or d the nc ir n, W 5 ad ed 5% nitrided method used in melting the iron. Where an eleciron powder. The resulting product was cast in tric furnace using induction heating is used to the usual manner and after solidification the bar melt the cast iron it is convenient to add'nitrided' was. heatedfor 10 hours at 1700 F. Practica y iron powder orother solid nitrogen compound t no decomposition of iron carbide resulted. Simithe molten cast iron therein. If desired to uselar cast iron without the nitrogen treatment ammonia gas as the nitrogen compound it may be when similarly heat-treatedhas substantially all passed or bubbled through the molten cast iron of the massive iron carbide decomp ed. I in the electric furnace. For this purpose, a i The nitrogen treatment may be usedto stabilize quartz tube may have one end immersed below and increase the depth of the chilled zone-in a V the surface of the molten iron and ammonia gas grey iron al'ticle rwhich has been cast against aunder slight pressure may be passed through the: chill. V quartz tube and discharged into the molten iron The following table indicates the effect on the below the surface thereof. -Where a cupola is depth of the chill 'on two cast irons with and used to melt the iron, ammonia gas conveniently without addition of. iron nitride to the molten.

may be introduced in the cupola blast. The nitrogen containing compound may be added to the molten cast iron, also, in the ladle prior to casting. Anyother suitable method of adding.

the nitrogen, compound may be used.

After the molten cast iron has been treated with the nitrogen compound it is thereafter. cast into molds in the same way that iron castings are iron. The several irons were fused in an induction furnace and chill bars 4" r; 4" .x -"were poured in green sand molds with a steel chill 1" x 1": 4" along the edge of thebar opposite All of the bars numbered 1 to 4 were poured at a temperature of 2 620 F. The. maximum tem. perature before pouring bars lto 4 were 2 832 F., 2823" F., 2787 F. and 2794" F., respectively.

In general it is contemplated that the comiron to producejwhite iron from compositions that would otherwise form grey or mottled irons. Various changesin" the modifications oi the I invention described herein may be made without ing the cast iron, adding to the molten cast iron position for grey iron articles having a chilled zone will be composed about as follows: carbon 3.00 3.'75%, silicon 0.50 2.50%, manganese 0.30 1.00%, sulphur 0.15% maximum, phosphorus 0.10;-0.50%, nitrogen in amount resulting from the addition of about .5 to- 1.00% nitrided iron powder, or by passing NH: gas through about 17 pounds of molten metal for. about 4 to 12 minutes at a rate oif about 12cubic feet per hour, balance iron.

A composition that may be usedior valve tappets is composed about as followst carbon 3.40%, silicon 2.00%, manganese 0.40%, sulphur 0.12%, phosphorus 0.15%, nitrogen as above. balance iron.

departingfrom the principles oi! the invention and I do notintend to limit the patent granted thereon except as necessitated by the prior art.

Iclaim: 1. The method of treating a cast iron to increase its resistance to heat which includes melta small amount. of a compound containing nitrogen, and castingthe thus treated cast iron into a mold, saidcast'iron when solidified containing iron carbide characterized by its stability under high temperature as compared with that in similar cast irons not treated with the nitrog n compound.

2. The method of treating a cast iron to increase its resistance to heat which includes melting the cast iron, adding to the molten cast iron a small amount of iron nitride, and casting the cast iron as thus treated into a mold, said cast treated with iron nitride.

A car wheel having a chilled surfac'emay be composed about as follows: c'arbon3.40%, silicon 0.65%.:mahganese 0.60%, sulphur 0.10%, phosphorus 0.15%, nitrogen as above, balance iron.

It has been found that cast iron. p oduced bytheaddition to the molten metal of 'nitrided iron powder is morcresistant to carbide decomposition at high temperatures than'similar, cast irons treated by bubbling ammonia gas therethrough.

Advantage may be taken or the method oi the invention to produce heat resistant white cast irons from compositions that without the treatmerit with nitrogen containing compounds would produce grey or mottled fractures. For example,

the proportions of. carbon and/orsilicon are limited inusual'practice by the fact that the cast ironwill be mottled or grey if either or both are above a certain amount. The limit dependson the rate of cooling of the molten iron in solidity-'- ing and this is related to the-size of section cast and on the type of mold used. By bubbling a small amount of ammonia through a molten cast ironof a: composition that under usual cooling conditions will Produce a grey or mottled cast iron, an iron having a white fracture .may' be produced that is resistant to carbide decomposi tion at high temperatures. V Y a As an example, a cast iron composition containing about 2.68% carbon, 1.07% silicon,'0.3'l%

' manganese, when melted in an electric furnace.

and cast into a green'sand mold will produce a grey or mottled iron in sections equivalent in size to a two inchround. -A similar composition through which a small amount oi ammonia has beenbubbled while the iron is molten, will pro'' duce a white iron when cast under similar conditions. In place of bubbling ammonia gas through the molten iron, other compounds cone taining nitrogen may be added to the molten iron when solidified containing iron carbide characterized byits stability under high temperature as compared with that in similar cast irons not 3. The methodof treating a cast iron to increase its resistance to heat which includes melting the cast iron, adding to the molten cast iron a small amount upto about 1.00% of iron nitride,

and casting the cast iron as thus treated into a mold, said cast iron when solidified containing iron carbide characterized by its stability under high temperature as compared with that in similar cast irons not treated with iron nitride.

4. The methodoif treating a cast iron to increase its resistance to heat which includes melting the castiron, bubbling through the molten cast iron a relatively small amount of ammonia gas, and casting the cast iron' as thus treated into a mold,said cast ironwhen solidified conta'iningiron carbide characterized by its stability under high temperature as compared with that in similar cast irons not treated with ammonia gas.

5. The method of producing a heat resistant cast iron article which includes melting iron in a cupola, introducing a small amount of ammonia gas in the cupola blast to thereby treat the molten iron with ammonia, and casting said treated molten iron into a mold to form a heat resistant cast. iron article, said cast iron being characterized by its resistance to carbide decomposition under high temperature as compared with generally similar cast irons not treated with ammonia gas.

6. The method of treating a cast iron to increase its resistance to heat which includes fusing a cast iron containing about 2.50-3.75% carbon, 0.50-2.50%' silicon, and 0.30-1.00% manganese, adding to the molten-cast iron a relatively small amount of a compound containing nitrogen, and

casting, the thus treated cast iron into a mold,- said cast iron when solidified containing iron carbide characterized ,byits stability under high temperature as compared with that in similar cast ironsanot treated with the nitrogen compound.

'7. The methodof producing a heat resistant white iron casting which includes fusing a cast iron that'would produce a grey or mottled iron casting when cooled normally and adding thereto a small buteflective amount of a compound containing nitrogen thereby producing a heat resistant white iron casting.

8. A cast iron containing a small but eilective 11. A heat resistant white iron casting containing 2.50-3.00% carbon, LOO-1.20% silicon,

0.30-0.457 manganese and a small but effectiveamount of nitrogen distributed throughout the casting.

12. A casting having a grey iron .core and a white iron surface zone, said casting having a small amoun of nitrogen substantially uniformly distributed t roughout the casting and having a. thicker zone of white iron than similar compositions containing no nitrogen.

13; The method of producing a casting having a greyiron core and a white iron surface layer whichacomprises fusing a cast iron composition, adding a, small amount of a nitrogen compound to sai used cast iron, and pouring the composition in a mold having ametai chill.

14.'The method of producing a casting which comprises providing a fused composition containing about 2.50-3.75% carbon, 0.50-2.50% silicon, 0.30-1.00% manganese, balance iron and ordinary impurities. and adding to the fused composition a small but effective amount up to about 1.00% of nitrided iron powder.

15. A'heat resistant iron casting containing about 2.50-3.75% carbon, 0.50-2.50% silicon, 0.30-1.'00% manganese and a small but effective amount of nitrogen equivalent in effect to that resulting from the addition of up to 1.00% of nitrided iron, or by passing NH: gas through about 17 pounds of molten metal for about 4 to 12 minutes at a rate of 12 cubic feet per hour.

16. The method of producing a cast iron prodnot containing iron carbide characterized by its stability under the influence of heat which includes, fusing a cast iron containing about 2.50-

3.75% carbon, 0.50-2.50% silicon, and 0.30-1.00% manganese, adding to said fused cast iron a small but effective amount up to about 1% of nitrided iron powder, and pouring the treated fused cast .iron into a mold to produce a cast iron product containing iron carbide characterized by its stability under the influence of heat.

17. The method of producing an iron casting which includes providing a fused cast iron containing about 2.50-3.75% carbon, (LSD-2.50% silicon, 0.301.00% manganese, balance iron and ordinary impurities found in cast iron, passing ammonia gas at a rate of 12 cubic feet per hour for from 4 to 12 minutes through about 17 pounds of the fusedcast iron, and casting the fused cast iron as thus treated into a mold to thereby produce a cast iron product characterized by its sta bility under high temperature as compared with similar products not treated with the ammonia gas.

ALFRED L. BOEGEHOLD. 

